asterisk users - Apr 2007 - "jittershrinkrate" equivalent in current (new) iax jb implementation

hello, is there any equivalent, that is currently usefull, if I have 
some iax connections with jitter spikes and another with minimal jitter?
for my jittery connections, I don't like to shrink jitter buffer too 
fast, because another jitter spike can occur again and small jb can't 
cover it.
as I read, in older iax jb implementation, this can be solved using 
"jittershrinkrate=" option, why it was currently removed?  :-\
PJ